Sears John S, Sherrill C David
Center for Computational Molecular Science and Technology, School of Chemistry and Biochemistry, Georgia Institute of Technology, Atlanta, Georgia 30332-0400, USA.
J Chem Phys. 2006 Apr 14;124(14):144314. doi: 10.1063/1.2187974.
Using single- and multireference approaches we have examined many of the low-lying electronic states of oxo-Mn(salen), several of which have not been explored previously. Large complete-active-space self-consistent-field (CASSCF) computations have been performed in pursuit of an accurate ordering for the lowest several electronic states. Basis set and relativistic effects have also been considered. For the geometry considered, our best results indicate the ground spin state to be a closed-shell singlet, followed by a pair of low-lying triplet states, with additional singlet states and the lowest quintet state lying significantly higher in energy. Hartree-Fock and density functional theory (DFT) results are obtained and are compared to the more robust CASSCF results. The Hartree-Fock results are qualitatively incorrect for the relative energies of the states considered. Popular density functionals such as BP86 and B3LYP are superior to Hartree-Fock for this problem, but they give inconsistent answers regarding the ordering of the lowest singlet and triplet states and they greatly underestimate the singlet-quintet gap. We obtained multiple Hartree-Fock and DFT solutions within a given spin multiplicity, and these solutions have been subjected to wave function stability analysis.
我们使用单参考和多参考方法研究了氧代锰（salen）的许多低电子态，其中一些此前尚未被探索过。为了精确排列最低的几个电子态，我们进行了大规模的完全活性空间自洽场（CASSCF）计算。同时也考虑了基组和相对论效应。对于所考虑的几何结构，我们的最佳结果表明基态自旋态为闭壳单重态，其次是一对低能三重态，其他单重态和最低的五重态能量则显著更高。我们获得了哈特里 - 福克（Hartree - Fock）和密度泛函理论（DFT）的结果，并与更可靠的CASSCF结果进行了比较。对于所考虑的态的相对能量，哈特里 - 福克结果在定性上是不正确的。诸如BP86和B3LYP等常用密度泛函在这个问题上优于哈特里 - 福克，但它们对于最低单重态和三重态的排序给出了不一致的答案，并且极大地低估了单重态 - 五重态的能隙。我们在给定的自旋多重度内获得了多个哈特里 - 福克和DFT解，并对这些解进行了波函数稳定性分析。
